US4472720A - Area navigational system using geosynchronous satellites - Google Patents

Area navigational system using geosynchronous satellites Download PDF

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US4472720A
US4472720A US06/133,005 US13300580A US4472720A US 4472720 A US4472720 A US 4472720A US 13300580 A US13300580 A US 13300580A US 4472720 A US4472720 A US 4472720A
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satellite
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Thomas W. Reesor
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/02—Details of the space or ground control segments

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  • This invention relates to navigational systems. More particularly, this invention relates to navigational systems comprising a series of satellites positioned in geosynchronous orbit above the earth which transmits a radio carrier modulated by a tone to be received by mobile craft to obtain a geographical fix.
  • U.S. Pat. No. 3,384,891 discloses a navigational system having a ground station which transmits ranging signals to a satellite which, in turn, retransmits such signals to the mobile craft and the ground station.
  • the mobile craft repeats the ranging signals received from the satellite and retransmits them to the satellite which, in turn, retransmits them to the ground station.
  • the ground station receives both the transmissions of the repeated ranging signals from the satellite and measures the time interval therebetween. From this time interval, the ground station computes the range from a known position of the satellite to the mobile craft.
  • the same interrogation message is transmitted from the ground station to a second satellite at a different location to obtain two computed ranges from the mobile craft to two known positions of the satellites.
  • the two range measurements using two different satellites provides two circles whose intersection is the position of the mobile craft.
  • the method of repeating ranging signals to obtain a geographical fix requires an interrogation signal to be transmitted by the mobile craft. Such interrogation reveals the position of the mobile craft to others, and thus is undesirable.
  • the ranging method also requires a transmitter to be placed on the mobile craft. The requirement of such a transmitter increases the cost and reduces the reliability of the navigational system and is therefore also undesirable.
  • a further disadvantage of the ranging method is the possibility of an overload condition due to each satellite receiving interrogation signals on the same frequency from numerous mobile craft. Such an overload condition reduces the accuracy of the system and could possibly cause some mobile craft to lose complete navigational reference.
  • Conventional OMEGA receiving equipment designed for use by mobile craft generally contains stable oscillators which are individually phase-locked to the separate OMEGA signals received from three different terrestrial stations.
  • the equipment determines the position of the mobile craft by measuring the phase difference between the pairs of these phase-locked oscillators. Each measured phase difference corresponds to a difference in the distance between two terrestrial transmitters, and thus locates the mobile craft on a hyperbolic line of position on an OMEGA navigation chart, as is well known in the art. Phase measurements made between each different pairs of oscillators locate the mobile craft on the different hyperbolic lines of position, which intersect to identify the position of the mobile craft on the chart.
  • U.S. Pat. No. 3,789,409 (Easton) describes a navigational system comprising a series of satellites which transmit multi-frequency signals derived from the same oscillator.
  • the stable oscillator is phase synchronized with the receiver equipment on the mobile craft.
  • the equipment computes the phase differences between the signals received from the satellites and the signals produced within the receiver to determine the distance between the mobile craft and the satellites. Hyperbolic lines of positions can then be plotted, and the position of the mobile craft determined.
  • a major problem associated with the above systems is the necessity of synchronizing the phase of the receiver equipment signals to the phase of the transmitter equipment.
  • Atomic clocks are being utilized to help overcome such a problem. More particularly, the Easton patent and U.S. Pat. No. 3,643,259 (Enter) incorporate an atomic clock to provide such synchronization. It is readily apparent that a momentary failure of either the atomic clock in the receiver equipment on the mobile craft or in the transmitter equipment will render the system inoperable. Furthermore, the phase drift inherent in atomic oscillators would also render the system inaccurate. Thus, such a volatile and unstable system is most undesirable.
  • Another object of this invention is to provide a navigational system wherein the transmitter equipment does not interrogate the receiver equipment on the mobile craft and thus does not reveal the position of the mobile craft.
  • Another object of this invention is to provide a navigational system which obviates the need for atomic clocks to provide synchronization of the transmitter equipment and the receiver equipment on the mobile craft.
  • Another object of this invention is to provide a navigational system which is not volatile to loss of power or loss of synchronization.
  • Another object of this invention is to provide a navigational system for long distance navigation of mobile craft around the world.
  • Another object of this invention is to provide a navigational system for both surface mobile craft and airborne mobile craft.
  • Another object of this invention is to provide a navigational system which overcomes the altitude error associated with airborne mobile craft.
  • the invention may be incorporated into a navigational system for determining the position of a mobile craft on the earth.
  • the navigational system comprises a plurality of satellites, preferably eight satellites, which are uniformly positioned in geosynchronous orbit about the equator of the earth.
  • the transmissions from each satellite comprise a radio carrier which is modulated by one or more tones, each carrier being of a different frequency for each satellite.
  • the receiver placed on the craft receives transmissions from two of the satellites and demodulates the carrier to recover a first and a second tone.
  • the phases of the two tones are compared with each other to define a hyperbolic line of position (LOP) on the surface of the earth.
  • LOP hyperbolic line of position
  • the receiver on the craft receives transmissions from a third satellite and similarly demodulates the carrier to recover a third tone.
  • the phase of the third tone is similarly compared with either the first or the second tone to define a second hyperbolic LOP on the surface of the earth.
  • the intersection of these two hyperbolic LOPs enables the mobile craft to obtain a geographical fix on the earth. It is noted that the intersections of the two hyperbolic LOPs actually define two fixes; one north of the equator and one south of the equator. Normally, however, such an ambiguity between the north and south latitudes is insignificant for most navigational purposes.
  • the navigational system comprises a means to accurately control the phase timing of each of the tones transmitted by each satellite.
  • the phase control means comprises a master tone oscillator located on one of the satellites, hereinafter called the master satellite.
  • the master satellite transmits a reference tone produced by the master tone oscillator to the two neighboring satellites, hereinafter called the slave satellites.
  • Each of the slave satellites then relays the reference tone to their neighboring slave satellite. This procedure is continued until all seven of the slave satellites have received the reference tone.
  • each of the satellites Due to the geosynchronous orbits of the satellites, the distance between each of the satellites is known, and thus the phase of the reference tones received by each of the slave satellites is adjusted accordingly to have identical phases. Each satellite is therefore able to transmit a different carrier frequency which is modulated by reference tones being in phase with one another.
  • the navigational system may comprise a second embodiment of the means to accurately control the phase timing of each of the tones transmitted by each satellite.
  • This second embodiment may comprise a plurality of ground stations which correspond to the plurality of satellites. The ground stations receive transmissions from the satellites and compare the phases of the transmitted tones with a reference tone. If the tones are not identically in phase, the ground stations transmit a correction signal to the satellite for correction of the phase of the transmitted tone. The phases of the transmitted tone from the satellites would then be synchronized with one another. The mobile craft is then able to obtain a geographical fix by receiving transmissions from at least three of the satellites and comparing the phases therebetween.
  • the drift correction means comprises a receiver located on the surface of the earth which receives transmissions from at least two satellites.
  • a comparator compares the phase of such transmissions with a position reference to produce an error signal.
  • An error correction computer receives the error signal and computes a correction signal which is transmitted to a correction receiver located on the master satellite.
  • the correction receiver utilizes such a correction signal to reposition the satellites in their proper orbit.
  • the means for repositioning the satellites is well known in the art and may comprise positioning rockets which are actuated to force the satellites back into the proper geosynchronous orbit.
  • the receiver located on the mobile craft is tuned to three frequencies to receive transmissions from three of the satellites.
  • the receiver of the mobile craft demodulates the carrier frequencies to obtain the reference tones.
  • the phases of the tones are then compared to obtain two geographical LOPs.
  • a position computer computes the intersection of the geographical LOPs and displays the intersection in terms of longitude and latitude.
  • the craft will appear to be at a higher latitude as seen from the satellites than when the craft is on the surface of the earth.
  • This error is approximately equal to A (tan ⁇ ), where A equals the aircraft's altitude and ⁇ equals the aircraft's latitude.
  • the error may be compensated by a tangent computer which computes the tangent of the latitude signal received from the position computer mentioned previously. The tangent computer then provides such signal to an altitude error computer.
  • an altitude error computer receives an altitude signal from an encoding altimeter located on the aircraft.
  • the altitude error computer then multiplies the altitude signal with the output of the tangent computer.
  • An error corrector subtracts the signal from the altitude error computer from the latitude signal received from the position computer.
  • the resulting corrected latitude signal along with the longitude signal is then displayed by the display means mentioned previously.
  • FIG. 1 is a perspective view of the satellites of the navigational system disposed uniformly in geosynchronous orbit above the equator of the earth;
  • FIG. 2 illustrates the intersection of the hyperbolic lines of positions on the surface of the earth
  • FIG. 3 is a plan view of the first embodiment of the phase control means
  • FIG. 4 is a block diagram of the electrical components of the master satellite
  • FIG. 5 is a block diagram of the electrical components of the slave satellites
  • FIG. 6 is a block diagram of the electrical components of the receiver equipment located on the mobile craft
  • FIG. 7 is a plan view of the second embodiment of the phase control means
  • FIG. 8 is a block diagram of the electrical components of the satellites of the second embodiment.
  • FIG. 9 is a block diagram of the electrical components of the ground station of the second embodiment of the phase control means.
  • FIG. 10 is a plan view of the third embodiment of the invention.
  • FIG. 11 is a block diagram of the electrical components of the master satellite of the third embodiment.
  • FIG. 12 is a block diagram of the electrical components of the ground station of the preferred embodiment of the invention.
  • FIG. 13 illustrates the error associated with airborne mobile craft
  • FIG. 14 is a block diagram of the electrical components of the means to correct the error associated with airborne mobile craft.
  • This invention is a navigational system 10 which comprises a plurality of satellites 12, preferably eight satellites 12A, 12B, 12C, 12D, 12E, 12F, 12G and 12H, which are uniformly positioned in geosynchronous orbit about the equator 14 of the earth 16.
  • a mobile craft 18 determines its position relative to the earth 16 by receiving transmissions from three of the satellites 12.
  • FIG. 1 illustrates the first embodiment of the navigational system 10 wherein the mobile craft 18 receives transmissions from the three satellites 12B, 12C and 12D.
  • Each transmission comprises a radio carrier which is modulated by one or more tones.
  • the receiver on the mobile craft 18 is tuned to receive each of the three different frequencies from the satellites 12B, 12C and 12D.
  • each of the tones which modulates the carrier frequencies is synchronized to have identical phases.
  • the receiver located on the mobile craft 18 receives transmissions from the satellites 12B and 2C.
  • the receiver demodulates the tones from such transmissions and compares the phase difference therebetween.
  • phase difference defines a first hyperbolic line of position (LOP) 20 on the surface of the earth 16.
  • LOP hyperbolic line of position
  • the receiver on the mobile craft 18 receives transmissions from the satellites 12C and 12D, demodulates the tones contained therein, and compares the phase difference therebetween to define a second hyperbolic LOP 22.
  • the intersections of the first and the second hyperbolic LOPs 20 and 22 define two geographical fixes; one fix 24 north of the equator 14 and a second fix 26 south of the equator 14.
  • the position of the mobile craft 18 is therefore determined provided the mobile craft 18 already knows whether it is north or south of the equator 14.
  • the navigational system 10 comprises means to accurately control the phase of each of the tones transmitted by each of the satellites 12.
  • the first embodiment of the phase control means comprises a master tone oscillator 30 located on one of the satellites 12, hereinafter called the master satellite 12A.
  • the master tone oscillator 30 produces a reference tone which is used to synchronize the phase of the tones which modulates the radio carrier frequencies of the remaining seven satellites 12B, 12C, 12D, 12E, 12F, 12G and 12H, hereinafter called slave satellites.
  • the master satellite 12A comprises two slave transmitters 32 and 34 which transmit the reference tone to the neighboring slave satellites 12B and 12H, respectively.
  • FIG. 5 shows a block diagram of the electrical components of each of the slave satellites 12B, 12C, 12D, 12E, 12F, 12G and 12H.
  • a slave receiver 36 receives the reference tone transmitted by the slave transmitter 34 and produced by the master tone oscillator 30.
  • the reference tone is provided to a phase synchronizer 39 which synchronizes the slave tone oscillator 38 with the master tone oscillator 30. It is noted that because the distance between the master satellite 12A and the slave satellite 12B is known, the propagation delay of the transmission from the master tone oscillator 30 can be determined.
  • the phase of the reference tone received by the slave receiver 36 can thus be compensated accordingly such that the reference tone supplied to the phase synchronizer 39 is identical to the phase of the reference tone produced by master tone oscillator 30.
  • the reference tone received by the slave satellite 12B is transmitted by a slave transmitter 40 to a neighboring slave satellite 12C.
  • Slave satellite 12C comprises electrical components as shown in FIG. 5, and thus receives the reference tone transmitted by slave satellite 12B and relays such reference tone to the next neighboring satellite 12D.
  • slave satellite 12D receives the reference tone transmitted by slave satellite 12C and relays the reference tone to slave satellite 12E.
  • slave transmitter 32 of the master satellite 12A transmits the reference tone from the master tone oscillator 30 to slave satellite 12H.
  • Slave satellite 12H relays the reference tone to slave satellite 12G which, in turn, relays the reference signal to slave satellite 12F.
  • All of the slave satellites 12B, 12C, 12D, 12E, 12F, 12G and 12H therefore receives the reference tone produced by the master tone oscillator 30.
  • the slave tone oscillator 38 in each of the slave satellites 12B, 12C, 12D, 12E, 12F, 12G and 12H are thus synchronized with one another by means of their phase synchronizer 39 to produce tones having identical phases.
  • the output of the master tone oscillator 30 of the master satellite 12 is frequency modulated by modulator 42 and then transmitted by transmitter 44 to the earth 16.
  • the outputs of each of the slave tone oscillators 38 in each of the slave satellites 12B, 12C, 12D, 12E, 12F, 12G and 12H are frequency modulated by modulator 46 and transmitted by transmitter 48 to the earth 16.
  • FIG. 3 illustrates, by way of example, the mobile craft 18 receiving transmissions from the master satellite 12A and slave satellites 12B and 12H.
  • the receiver equipment which receives and determines the geographical LOPs is shown in FIG. 6. More particularly, the receiver equipment comprises three receivers 50A, 50B and 50C which are respectively tuned to receive the radio carrier transmitted by satellites 12H, 12A and 12B. Receivers 50A and 50B demodulate the radio carrier from satellites 12H and 12A to recover a first and a second tone. The phases of the two tones are then compared by means of a phase comparator 52.
  • the difference in the phases are then supplied to a computer 54 to compute a first hyperbolic LOP.
  • the output of computer 54 is then supplied to a position computer 56.
  • the receiver 50C demodulates the radio carrier received from satellite 12B to recover a third tone.
  • the phases of the second and third tones are then likewise compared by means of comparator 58.
  • the difference in the phases are then supplied to a computer 60 which computes a second hyperbolic LOP.
  • the output of computer 60 is supplied to position computer 56.
  • the position computer 56 determines the intersection of the first and second hyperbolic LOPs and transforms such intersection in terms of a longitude signal 62 and a latitude signal 64.
  • a display means 66 receives the longitude and latitude signals 62 and 64 and displays such signals numerically. The position of the mobile craft 18 is thus determined in terms of latitude and longitude.
  • FIGS. 7-9 a second embodiment of the means to accurately control the phase of the reference tones is shown in FIGS. 7-9.
  • eight satellites 68 are uniformly positioned in geosynchronous orbit above the equator 14 of the earth 16.
  • Each of the satellites 68 comprises a tone oscillator 70 which produces a reference tone which is frequency modulated by modulator 72.
  • the output of modulator 72 is then transmitted by transmitter 74 to the earth 16.
  • the receiver equipment located on the mobile craft 18 is similar to the receiver equipment as discussed previously and as shown in FIG. 6. Accordingly, determination of the geographical fix the mobile craft 18 is similar to the method discussed previously.
  • the phase control means of FIGS. 7-9 comprises a plurality of ground stations 76 positioned on the surface of the earth 16. Each ground station 76 comprises three receivers 78 which are tuned to receive transmissions from three of the satellites 68A, 68B and 68C.
  • a demodulator 80 demodulates the radio carries thus received to obtain the three tones contained therein. The phases of the tones are then supplied to a comparator 82. Comparator 82 compares the differences in the phases of each tone with a reference phase supplied by phase reference 84 and produces an error signal 86 which is supplied to an error correction computer 88.
  • Computer 88 computes a correction signal 90 which is transmitted by transmitter 92 to the three satellites 68A, 68B and 68C.
  • Each of the satellites 68 comprises a correction receiver 94 which receives the correction signal 90.
  • the output of the correction receiver 94 is connected to a phase synchronizer 95 which synchronizes the phase of the tone produced by the tone oscillator with the reference phase produced by phase reference 84 in accordance with the correction signal 90 thus received.
  • a phase synchronizer 95 which synchronizes the phase of the tone produced by the tone oscillator with the reference phase produced by phase reference 84 in accordance with the correction signal 90 thus received.
  • FIGS. 10-12 illustrates such a correction means.
  • the correction means is utilized in conjunction with the first embodiment of the phase control means as illustrated in FIGS. 1-6.
  • the master satellite 12A comprises a master tone oscillator 30 which produces a reference tone which is transmitted to the neighboring slave satellites 12B and 12H by slave transmitters 34 and 32, respectively.
  • the slave satellites 12B and 12H then relay the reference tone to the remaining slave satellites as discussed previously.
  • the output of the master tone oscillator 30 is frequency modulated by modulator 42 and transmitted to the earth 16 by transmitter 44. Such transmission is received by a ground station 96 located on the surface of the earth 16.
  • the ground station 96 comprises a receiver 98 which is tuned to the carrier frequency of transmitter 44 and to the carrier frequency of a slave satellite 12B.
  • the output of receiver 98 is demodulated by demodulator 100 to recover the phase of the reference tones.
  • the phases of such tones are supplied to comparator 102.
  • a position reference means 104 supplies a reference phase corresponding to the particular location of the master satellite 12A to the comparator 102. Comparator 102 compares the difference between such phases and produces an error signal 106 therefrom.
  • the error signal 106 is supplied to an error correction computer 108 which computes a correction signal 110 which is then transmitted by transmitter 112 to the master satellite 12A.
  • the correctional signal 110 is received by a correction receiver 94 of the master satellite 12A.
  • the correction receiver 94 determines from the correction signal 110 the appropriate action which must be taken in order to place the master satellite 12A into its proper geosynchronous orbit.
  • the correction receiver 94 could actuate positioning rockets 115 which force the master satellite 12A into a proper orbit.
  • the correction signal 110 is further supplied to the master tone oscillator 30 to be transmitted by the slave transmitters 34 and 32 to the neighboring slave satellites 12B, 12C, 12D, 12E, 12F, 12G and 12H. Accordingly, all of the slave satellites could then be repositioned into their respective proper geosynchronous orbit by means of similar positioning rockets.
  • the correction means 117 is located on the craft 18 and comprises the latitude signal 64 determined by the position computer (see FIG. 6) being supplied to a tangent computer 116 for computation of the tangent of the latitude signal 64.
  • the output of the tangent comparator 116 is then supplied to an altitude error computer 118. Simultaneously, the altitude signal output 120 of an encoding altimeter 122, which is commonly found on most aircraft, is supplied to the altitude error computer 118.
  • Computer 118 multiplies the tangent of the latitude signal 64 with the altitude signal 120 and supplies the result to an error corrector 124.
  • the error corrector 124 subtracts the output of the altitude error computer 118 to the latitude signal 64 to determine a corrected latitude signal 126 which is supplied to the display 66. Accordingly, display 66 displays the longitude signal 62 and the corrected latitude signal 126.
  • pulse modulation could alternatively be used. More particularly, the timing of the pulses between the satellites 12 could be carefully controlled enabling the receiver equipment on the mobile craft 18 to measure such pulse timing received from three of the satellites 12 for defining hyperbolic LOPs to obtain a geographical fix. Each satellite 12 would transmit such pulses on a separate frequency such that the receiver equipment on the mobile craft 18 could determine which satellite 12 is being received. Accordingly, the use of pulse modulation in lieu of frequency modulation does not depart from the spirit and scope of this invention.

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US4601005A (en) * 1981-12-31 1986-07-15 The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland Receivers for navigation satellite systems
US4647935A (en) * 1984-12-06 1987-03-03 Starnav Corporation Apparatus for determining the magnitude of phase discontinuities introduced into a received signal at known instants
EP0171751A3 (en) * 1984-08-16 1988-07-13 Communications Satellite Corporation Position determination and message transfer system employing satellites and stored terrain map
FR2645954A1 (fr) * 1989-01-11 1990-10-19 Mitsubishi Electric Corp Procede de determination d'une position utilisant des satellites
US4965586A (en) * 1984-08-16 1990-10-23 Geostar Corporation Position determination and message transfer system employing satellites and stored terrain map
US5017926A (en) * 1989-12-05 1991-05-21 Qualcomm, Inc. Dual satellite navigation system
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US9632503B2 (en) 2001-04-18 2017-04-25 Space Data Corporation Systems and applications of lighter-than-air (LTA) platforms
US9643706B2 (en) 2001-04-18 2017-05-09 Space Data Corporation Systems and applications of lighter-than-air (LTA) platforms
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Cited By (54)

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Publication number Priority date Publication date Assignee Title
US4601005A (en) * 1981-12-31 1986-07-15 The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland Receivers for navigation satellite systems
EP0171751A3 (en) * 1984-08-16 1988-07-13 Communications Satellite Corporation Position determination and message transfer system employing satellites and stored terrain map
US4839656A (en) * 1984-08-16 1989-06-13 Geostar Corporation Position determination and message transfer system employing satellites and stored terrain map
US4965586A (en) * 1984-08-16 1990-10-23 Geostar Corporation Position determination and message transfer system employing satellites and stored terrain map
US4647935A (en) * 1984-12-06 1987-03-03 Starnav Corporation Apparatus for determining the magnitude of phase discontinuities introduced into a received signal at known instants
FR2645954A1 (fr) * 1989-01-11 1990-10-19 Mitsubishi Electric Corp Procede de determination d'une position utilisant des satellites
US5017926A (en) * 1989-12-05 1991-05-21 Qualcomm, Inc. Dual satellite navigation system
US5126748A (en) * 1989-12-05 1992-06-30 Qualcomm Incorporated Dual satellite navigation system and method
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